Many chemical reactions, such as the synthesis of organic compounds for pharmaceutical applications and the reformation of petroleum products, are catalyzed by strong acids. Representative industrially important types of acid catalyzed organic reactions include Friedel-Crafts alkylation and acylation of aromatic compounds, Schiff base formation from ketones and primary amines, acetal and ketal syntheses, and nitration of aromatic compounds. In the petroleum industry, the alkylation of olefins such as isobutene, for example, is a critical process for production of gasoline. Common mineral acids, such as sulfuric, nitric, hydrochloric, hydrofluoric and phosphoric acids, have long been employed in these chemical reactions, but have well recognized drawbacks. For example, these deficiencies include the need to employ wasteful and expensive rigorous supplemental separation processes because the final product often must be scrupulously free of the acid or its salts. Also, shipping, handling and storage of industrial scale quantities of mineral acids present safety, environmental and security threats that require costly and productivity inhibiting countermeasures. Furthermore, some of these mineral acids, such as sulfuric and nitric acid, can oxidize reactants to form undesirable by-products. Due to these very serious shortcomings, there has been much interest in developing effective replacements for strong mineral acid catalysts.
Some commercially interesting polymeric strong acids are identified by the formula (1) in which n and m are mole fractions of the respective component in the polymer and x is an integer typically in the range of 0-3. These include compounds such as Nafion®-H and Aquivion® PFSA perfluoroalkanesulfonic acid resins that are heterogeneous in reaction media and thus can simply separate from product. Nafion®-H is a copolymer of tetrafluoroethylene (“TFE”) and a perfluorinated vinyl ether with pendant perfluoroalkylsulfonic acid group as shown in formula (1) and in which x=1. Aquivion® is a copolymer of TFE and a perfluorinated vinyl ether with the pendant perfluoroalkylsulfonic acid group shown in formula (1) in which x=0.

Also available are inorganic solid acids such as zeolites which can be employed as heterogeneous acid catalysts but are prone to fouling.
While heterogeneous catalysts offer to facilitate separation, there are no known significant commercial applications using Nafion® copolymer as an acid catalyst. This may be attributable to low activity relative to traditional, liquid strong acids. Reduced activity results from the low surface area of Nafion® particles and the polymer's inability to swell in most solvents. These factors render most of the acid moiety sites inaccessible to the reactants. Entrapping Nafion®-H within silica gel pores increases the surface area and has been attempted to increase activity. However, plugging of the pores is a common feature of most solid, heterogeneous acid catalysts and can significantly diminish activity.
Acid catalysts based on porous, sulfonated crosslinked polystyrene resins are in common use. See Harmer 2001, Applied Catalysis A: General 221, 45-62. These polymers lack the thermal and chemical stability of the perfluoropolymers and have an acid strength several orders of magnitude less than perfluoroalkylsulfonic acids. They also are subject to loss of activity due to pore plugging.
Non-polymeric, highly fluorinated acid catalysts, such as trifluoromethanesulfonic (“triflic”) acid and perfluorooctanesulfonic acid are known as “super acids” because they are orders of magnitude stronger acids than sulfuric acid. Table 1 compares triflic acid strength to sulfuric and acetic acids. Thus, these super acids can be more effective homogeneous catalysts than mineral acids, and can catalyze transformations that standard mineral acids cannot accomplish. Although small molecule perfluorinated acids also have high thermal and chemical stability and are not active oxidizing agents, they do have significant disadvantages. For example, triflic acid is a toxic liquid with boiling point of 162° C. It can cause blindness on eye contact and severe burns on the skin. Longer chain non-polymeric perfluorosulfonic acids, such as perfluorooctane sulfonic acid, are toxic and highly persistent in the environment such that they are readily taken up by and are enduring in living organisms. These characteristics have led to regulations or bans on their use. Consequently, there remains a need for acid catalysts that can dissolve in reaction media for efficient utilization, have stable, superacid strength, can be readily separated from the reaction medium, and are more environmentally benign than traditional strong acid catalysts.
TABLE 1AcidFormulapKa*trifluoromethanesulfonicCF3SO3H−14  (“triflic”) acidsulfuric acidH2SO4−3.0acetic acidH3COOH 4.8*acid strength inversely proportional to pKa value
Watakabe et al., U.S. Pat. No. 7,220,508 and Squire, U.S. Pat. No. 4,935,477 disclose copolymers from perfluorinated cyclic monomer, perfluoro-2,2-dimethyl-1,3-dioxole (“PDD”), and a perfluorinated vinyl ether, “SEFVE” (see Table 2, below). In sulfonic acid form, this polymer can be dissolved or well dispersed in organic solvents having hydroxyl groups. Solubility in other organic solvents is not disclosed. Perry et al., US Patent Application 2013/0245219 disclose copolymers of PDD and other cyclic fluorinated monomers with perfluorinated vinyl ethers of formula CF2═CFO[CF2]nSO2X wherein n is 2, 3, 4 or 5 and X is F, Cl, OH or OM wherein M is a monovalent cation. The use of solutions of these perfluorinated polymers for acid catalysis is not disclosed.